Jean BERNARD * I should like to begin with an assumption and a paradox. The assumption is that leukemia is a disease of a stem cell characterized by pathologie alterations of that cell and its progeny. All present research and discussions are centered around the leukemic cell. So is this symposium, which would not take place except for our primary interest in the leukemic cell. This does not preclude, of course, consideration of other definitions and other approaches to the prOblem. By definition, then, the leukemic cells are abnormal cells and their metabolism and functions are presumed to be abnormal. Yet, the classification of the different types of leukemias is based upon the characteristics of normal cells. We talk of "lymphoblasts" and "myeloblasts" as predominant cell types in leukemia. This leads to a double paradox. In the first pi ace it is clearly illogical to classify abnormal cells by their resemblance to normal cells, since their very abnormality consists in not being normal. Yet, as a second paradox, the classifica ti on has had the happy consequence of ai ding us in the treatment and prognosis of leukemia for the past 25 years. A more detailed analysis shows that the consequence of this paradox are complex: while there exists a useful correlation between cellular types, treatment and prognosis, numerous problems and difficulties persist. The most serious of them concems the "unclassified leukemias" which are the reason for this reunion.

Section I: Present Practice of Classification, its Utility and Limitations

Cytological Classification of Acute Leukemias. A Survey of 1400 Cases
Classification of the Acute Leukemias
Leukemic Lymphosarcomas: Respective Prognosis of the Three Types: Prolymphocytic, Lymphoblastic (or Lymphoblastoid) and Immunoblastic
Search for Correlations between Cytological Types and Therapeutic Sensitivity of Acute Leukemias
Answers to Submitted Questions
Open Discussion of Section I
Section II: New Techniques Used in Cytological Diagnosis
Fluorescence Probe and Biochemical Characterization of Leukemic Cells
Discussion
Automated Cell Population Analysis
Discussion
The Use of B and T Membrane Markers in the Classification of Human Leukemias, with Special Reference to Acute Lymphoblastic Leukemia
Discussion
Volumetric Determinations of Blood Cells in Acute Lymphoblastic Leukemia
Discussion
Acute Leukemia Cytochemical Profile: Diagnostic and Clinical Implications
Discussion
B, T and "Null" Cell Leukemias. Electron Cytochemistry and Surface Morphology
Discussion
Giant Platelet Granules in Refractory Anemia (Preleukemia) and Myelomonocytic Leukemia: a Cell Marker?
Discussion
Inhibition of Time-dependent Enhancement of Amino Acid Transport by Leukemic Leukocytes: a Possible Index of the Sensitivity of Cells to Drugs
Discussion
Marrow Culture - a New Approach to Classification of Leukemias
Discussion
Cytogenetic Studies of Marrow and Peripheral Blood Granulocyte Colonies in Treated Chronic Myelogenous Leukemia (presented by G. Brecher) Discussion
Cytogenetic Studies in Preleukemia: Studies before and after Transition to Acute Leukemia in 17 Subjects
Discussion
Correlated Cytogenetic and Ultrastructural Studies in Acute Leukemia(Abstract)
Discussion
Section III: Pathophysiology of the Leukemic Cell
Pathology of the Leukemic Cell or Reasons Why Some Leukemias are Unclassifiable
Discussion
Abnormal Neutrophils in Acute Myelogenous Leukemia: Identification of Subpopulations Based on Analysis of Azurophil and Specific Granules (Read by G. Brecher)
Significance of Cell Differentiation in Acute Myeloid Leukemia
Discussion
Different Cell Proliferation Models in Myeloblasts and Lymphoblastic Leukemia. Contribution of Cell Kinetics to the Classification of Acute Leukemias
Discussion
Clonal Evolution and Progression in Chronic Myeloid Leukemia
Discussion
Variations of the Proliferative Activity of Leukemic Myeloblasts Related to the Stage of the Disease
Discussion
Section IV: Summary and General Discussion
Summing Up
Summing Up
On Classification of Leukemia
General Discussion.